North and South Korea trade fire across disputed maritime border

South Korea's Defence Ministry says the North fired around 500 artillery shells, around 100 of which landed within the South's side of the disputed maritime border.

The Defence Ministry spokesman in Seoul, Kim Min-Seok said the exercise was a "premeditated provocation and is an attempt to test our military's determination" to protect the maritime boundary.

"If the North takes issue with our legitimate returning of fire and uses it to make yet another provocation towards our sea and islands, we will make a resolute retaliation," he said.

The three-hour long North Korean drill triggered an exchange of fire as South Korea responded with volleys of shells into North Korean waters.

There has been no indication that the shelling by either side was aimed at any particular target.

South Korean officials said residents on the south's Baengyeong island, close to the maritime boundary, had taken shelter as a precaution.

North Korea earlier announced it would be carrying out a live-fire drill near the border, Seoul's defence ministry said.

"The North notified us that they would stage live-fire drills near the Yellow Sea border today," a ministry spokesman told AFP.

The South's Yonhap news agency said the North's notification had warned the South to "control" its naval vessels ahead of the drill.

It is unusual for North Korea to notify the South ahead of a live-fire exercise, and the announcement comes at a time of simmering inter-Korean tensions.

Pyongyang has carried out a series of rocket and short-range missile launches in recent weeks, in a pointed protest at ongoing annual South Korea-US military exercises.

On Wednesday it upped the ante by test-firing two mid-range ballistic missiles capable of striking Japan, sparking condemnation from the United Nations Security Council.

The de facto maritime boundary between the two Koreas - the Northern Limit Line - is not recognised by Pyongyang, which argues it was unilaterally drawn by the US-led United Nations forces after the 1950-53 Korean War.

The disputed border has been the scene of brief but bloody naval clashes in 1999, 2002 and 2009.